Conventionally, lithium ion secondary batteries have been widely used because smaller size and larger capacity can be promoted. In the lithium ion secondary battery, lithium is intercalated and deintercalated in the positive electrode and the negative electrode. Therefore, as materials constituting the positive electrode and the negative electrode, that is, active materials, materials capable of intercalating and deintercalating Li are used.
As the negative electrode active materials of lithium ion secondary batteries, carbon materials have conventionally been widely used. However, in recent years, negative electrodes using Si have attracted attention because of higher theoretical capacity than that of carbon. However, the volume of Si changes largely by the intercalation and deintercalation of lithium ions. Therefore, a problem is that the charge and discharge performance decreases during use.
The following Patent Literature 1 discloses a negative electrode material that is a spherical assembly formed by bonding plate-like Si materials, wherein pores are formed inside the assembly, in order to solve such a problem.